When electrical components are connected together, for example, to form a circuit board, the electrical components are very susceptible to various contaminants such as dirt and moisture, particularly if they are stored for a considerable period of time. Additionally, the components are subject to various contaminants and moisture and may be damaged when they are attached to a substrate such as a circuit board. To avoid this problem, coatings have been applied to cover the components or circuit board containing the electrical components.
The electrical components and/or circuit boards have been coated with organopolysiloxane compositions to protect the components from moisture, contamination and damage. However, it has been found that organopolysiloxane compositions which cure by the addition of silicon bonded hydrogen atoms to organopolysiloxanes having olefinic unsaturation in the presence of a platinum catalyst do not cure at the interface of the metallic connectors. It is believed that the no-clean flux, i.e., flux which is not removed after soldering electrical components, inhibits curing of these organopolysiloxane compositions.
Therefore, this invention relates to a platinum catalyst and a one-component organopolysiloxane composition containing a hydrosilation catalyst which may be applied to circuit boards and/or hybrid circuitry to form a curable coating thereon.
Organopolysiloxanes which are curable by the reaction of silicon-bonded, terminally unsaturated olefinic radicals and silicon bonded hydrogen atoms in the presence of hydrosilation catalysts such as platinum compounds and complexes thereof are well known and are disclosed, for example, in U.S. Pat. No. 3,419,593 to Willing and U.S. Pat. No. 4,450,283 to McAfee et al.
Platinum catalysts which have been employed to promote the hydrosilation reactions such as the addition of organosilicon compounds containing .tbd.SiH groups to organosilicon compounds containing aliphatic unsaturation are complexes such as described in U.S. Pat. No. 3,775,452 to Karstedt, in which an unsaturated organosilicon compound is reacted with a platinum halide and thereafter treating the resultant mixture with a base to remove the available inorganic halogen.
Another platinum complex which may be used in the hydrosilation reactions is described in U.S. Pat. No. 4,603,215 to Chandra et al., in which the platinum complex is prepared by reacting a platinum vinylsiloxane complex prepared in accordance with U.S. '593 to Willing and U.S. '452 to Karstedt. In general these platinum-vinylsiloxane complexes are prepared by contacting a vinylsiloxane such as described above with a platinum compound such as chloroplatinic acid (H.sub.2 PtCl.sub.6.6H.sub.2 O). The resultant platinum-vinylsiloxane complex is then contacted with an alkyne to form a platinum alkyne complex. Also, U.S. Pat. No. 3,445,420 to Kookootsedes et al., discloses an organopolysiloxane composition comprising a mixture of an olefin containing organosilicon polymer, an organosilicon compound containing silicon-bonded hydrogen atoms, a platinum catalyst and an acetylenic compound as an inhibitor.
One of the disadvantages of the organopolysiloxanes described above is that they must be mixed just prior to use. When inhibitors are incorporated in these compositions and they are stored for a period of time before use, they will not cure or will cure very slowly in the presence of no-clean flux.
Therefore, it is an object of the present invention to provide a one-component organopolysiloxane composition which cures in the presence of no-clean flux. Another object of the present invention is to provide a circuit board having a cured coating thereon. Still another object of the present invention is to provide a platinum catalyst which promotes curing of an organopolysiloxane composition in the presence of no-clean flux. A further object of the present invention is to provide a process for preparing a platinum catalyst which promotes the addition of .tbd.SiH groups to Si-bonded aliphatic unsaturated hydrocarbon groups. A still further object of the present invention is to provide a platinum catalyst which is not inhibited by no-clean flux.